The present invention relates generally to electrical switches and, more particularly to a sealed proximity switch for use with a movable member such as a valve stem.
A valve position switch, such as a limit switch, is used to indicate the state, e.g., closed or open, of a valve that controls the flow of fluids. Typically, the valve has a linearly or rotatably movable member whose relative position relates to the state of the valve. The switch contacts the movable member of the valve when the member attains a particular position typically corresponding to a fully open or fully closed valve. The switch then provides electrical indication to a remote controller as to the state of the valve.
Ideally, the switch is substantially durable to sustain repeated contact with the movable member throughout its life. Because the switch may be susceptible to corrosive elements or fluids that may destroy the sensor within the switch, it is desirable that the switch has ample protection, seals and a minimal number of openings.
One aspect of the present invention provides an electric device for indicating a position of a movable member. The electric switch includes an enclosure, a lever, a permanent magnet, a biasing member and a sensor. The enclosure has a hermetically sealed chamber defined by a first wall and an adjacent second wall. The lever is pivotally attached to the first wall and holds the permanent magnet adjacent the second wall. The magnet is movable with the lever between a first and a second position. The biasing member biases the lever and magnet to the first position. The sensor is located within the chamber and is capable of being influenced by the magnet when it is moved into the second position through contact of the lever with the movable member.
Another aspect of the present invention provides a limit switch for indicating the state of a valve. The limit switch includes an enclosure, an arm, a holder, a magnet, a biasing member and a sensor. The enclosure has a sealed chamber defined by a first wall and an adjacent second wall. The arm has one end pivotally attached to the first wall. A receptacle on the arm for holding the magnet adjacent to the second wall. The biasing member is disposed between the arm and the first wall of the enclosure. The sensor is disposed in the chamber adjacent to the second wall and is magnetically influencable to indicate the position of the valve member when the magnet is pivoted with the arm into an aligned relation with the sensor.
Yet another aspect of the present invention provides a method for indicating a predetermined position of a movable member. The method includes attaching one end of an arm to a first wall of an enclosure; holding a magnet on the arm adjacent to a second wall of the enclosure; sealing a sensor within the enclosure adjacent to the second wall; pivoting the magnet in relation to the sensor by contacting the movable member with the pivot arm; electrically indicating that the movable member has attained the predetermined position when the magnet is in an aligned relation to the sensor; and biasing the pivot arm and the magnet away from the aligned relation to the sensor when the movable member is not at the predetermined position.
The foregoing summary is not intended to summarize each potential embodiment or every aspect of the invention disclosed herein, but merely to summarize the appended claims.